During the early 19th century, when industrialization was just getting under way, water was the accepted liquid to power hydraulic systems. But with the development of more sophisticated hydraulic systems, water was pushed into the background as the need for viscosity and lubricity to prevent pump wear increased, and water was therefore replaced by petroleum hydraulic fluids.
However, the recent oil shortages and the tremendous increase in oil prices have brought about a renewed industrial interest in a water-based hydraulic fluid and brought about development of soluble oils consisting of a mixture of about 95% water and 5% oil dispersed in the water.
More recent restrictions brought about by the great interest in environmental control have further increased the interest in high water-based hydraulic fluids because many of such fluids are either biodegradable or easily disposed of; are fire resistant; and are compatible with other water-based products used as coolants.
However, because water, and even high water-based hydraulic fluids have the disadvantages of causing corrosion, and are low in viscosity and lubricity, the pumps designed to use these low-cost hydraulic fluids were extremely expensive and, even so, had materially shorter life spans than the pumps designed for use of oil only as the hydraulic fluid.
The present invention overcomes the disadvantages in pumps of prior design by providing a relatively low-cost gear pump that will work equally as well with oil or high water-based hydraulic fluids and, in the latter case have a usefull life as great as, if not greater than, gear pumps designed for use with oil only.
A feature of my improved pump is the use of a gear track insert located in the gear housing pressure-generating zone. This insert is made of a high-wear and abrasive-resistant material for long pump life, and may be easily replaced during a pump overhaul. Since the gear track insert absorbs most of the wear and abrasion in the pressure-generating zone, the more expensive gear housing is largely relieved of wear and therefore very rarely has to be replaced.
A further feature of my improved pump is the use of isolation seals to reduce or eliminate high pressure from leaking into the low pressure zone of the pump. These seals also control the pressure plate to gear face load to minimize wear and leakage. These, and other features, make my improved pump unique when compared to pumps of prior design.